What is Heap Pollution?
Heap pollution implies that we have bad data in our heap memory. In Java language, heap pollution is a situation that occurs when a variable of parameterized type points to an object that is not of that parameterized type.
How is Heap Pollution detected?
At the run-time, there is a chance of arising heap pollution that will cause ClassCastException. Heap pollution means the bad data in the heap memory. Here bad data is an object of type X but an object of type Y is expected and it will throw ClassCastException at runtime.
Lets understand the heap pollution with program:
Compile Time Console:
prog.java:12: warning: [unchecked] unchecked cast List listOfInteger = (List)(Object)listOfString; ^ required: List found: Object 1 warning
Exception in thread “main” java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
How to deal with Heap Pollution?
Compile Time Console:
prog.java:4: warning: [unchecked] Possible heap pollution from parameterized vararg type List public static void merge(List... stringList) ^ prog.java:23: warning: [unchecked] unchecked generic array creation for varargs parameter of type List merge(list1, list2, list3); ^ 2 warnings
Exception in thread "main" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String at Geeks.merge(File.java:10) at Geeks.main(File.java:23)
Note: If we don’t want warnings at the compiler time then we can use @SafeVarargs annotation above the method. If we know that the method doesn’t contain any heap pollution situation then you can annotate it with @SafeVarargs to suppress the warning. It does not mean that it will allow our code for heap pollution. It means that if in the code, there is a chance of Heap pollution, it will throw ClassCastException at the run time.
How to prevent Heap pollution situations?
We cant prevent Heap pollution situations, but we can follow a few rules that can help us to prevent heap pollution like:
- Don’t use varargs parameters with generic types or cast an Object array to an array of a generic type.
- Not to expose the varargs parameter or the generic array to any other method.
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